Apparatus for determining the magnetic condition of steel strip during continuous annealing



J. B. CAMP ETAL, 3,130,363 APPARATUS FOR DETERMINING THE MAGNETICCONDITION April 21, 1964 OF STEEL STRIP DURING CONTINUOUS ANNEALINGFiled June 8, 1960 3 Sheets-Skmeet l INVENTORS JAMES a. CA MP dad N momsE M: CABE By M 541mm Aprll 21, 1964 J. B. CAMP ETAL 3,130,363

APPARATUS FOR DETERMINING THE MAGNETIC CONDITION OF .STEEL STRIP DURINGCONTINUOUS ANNEALING Filed June 8. 1960 5 Sheets-Sheet 2 8 nvvnvrona JAM55 5. CAMPand' moms 5. Me me:

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" I106 L2 L I INVENTOHS JAMES 5. CA MP and THOMAS E. McCAB- W AffarneyUnited States Patent Ofiice 3,130,363 Patented Apr. 21, 1964 3,139,363ATPARATUS FUR DETERMINING THE MAG- NETIC CONDTTIQN OF STEEL STRIP DURINGCONTINUOUS ANNEALING James B. Camp and Thomas E. McCabe, Fairfield, Ala,

assignors to United States Steel Corporation, a corporation of NewJersey Filed June 8, 1969, Ser. No. 34,777 2 Claims. (Cl. 324-34) Thisinvention relates to apparatus for determining the magnetic condition ofmoving ship and more particularly for determining the condition of steelstrip being continuously annealed. The annealing furnaces are designedto heat a moving strip to about 1400 F., which is approximately at theCurie point of the strip, with the strip being held at this temperaturefor approximately 15 seconds. Prior to our invention attempts were madeto measure the strip temperature by optical measurements andthermocouples, but these proved to be unsatisfactory for determin ng thetrue temperature of the strip. As a result, the strip was often heatedhigher than necessary or lower than required to obtain a fully annealedproduct.

It is therefore an object of our invention to provide apparatus fordetermining the magnetic condition of a moving steel strip beingcontinuously heated so as to determine its temperature by relation toits Curie point.

This and other objects will be more apparent after referring to thefollowing specification and attached drawings, in which:

FIGURE 1 is a view of the strip passing through a continuous annealingfurnace;

FIGURE 2 is an enlarged sectional View taken on the line IIII of FIGURE1;

FIGURE 3 is a view, partly in section, of a valve used in our invention;

FIGURE 4 is a view taken at right angles to FIGURE 3 with parts beingbroken away and shown in section; and

FIGURE 5 is a schematic wiring diagram of the magnetic detector.

Referring more particularly to the drawings, reference numeral 2indicates the heating chamber of a continuous annealing furnace throughwhich strip S passes over conveyor rolls 4. A non-magnetic stainlesssteel tube 6 (such as Inconel) passes through walls 8 of the chamber 2below the strip S adjacent the entry end of the soak Zone. A packinggland 19 is fastened to outer steel plate 12 of the chamber 2 at eachend of the tube 6. Each of the packing glands consists of an innermember 14 welded to the plate 12, packing material 16 and an outermember 18 which holds the packing material in close engagement with thetube 6 and which is attached to member 14 by means of capscrews 29. Oneend of the tube 6 is closed by means of a plug 22 which is provided witha water outlet 24. The other end of the tube 6 is attached to a tube 26by means of a valve 28 which has proved to be particularly suited forthe intended purpose. The body of valve 28 includes plates 30R and 30Lwhich surround and are welded to tubes 6 and 26, respectively. A spacerplate 32 is provided between the plates 30R and 30L at the lower endthereof. Plate 32 extends inwardly almost to the tubes 6 and 26 and isprovided with a groove 34 therein which communicates with the outside ofthe plate 32 by means of a hole 36 which is normally closed by means ofa plug 38. A spacer plate 46 extends between the other ends of theplates 36R and 30L and is provided with a radial opening 42 throughwhich extends valve stem 44. Longitudinal spacer plates 45 are providedbetween spacer plates 32 and 40. The opening 42 is counterbored toreceive packing 46, packing gland 48 and nut 59, all of which areconventional. Plates 36R and 30L are connected by means of bolts 52,which pass through spacer plates 32,

4i) and 45. The inner end of valve stem 44 is connected to a gate 54which consists of three wedge plates 56, 58 and 60. Four threaded pins62 are secured to plates 56 and 69 and pass through elongated slots 64in center wedge member 58. Valve stem 44 is connected to center wedgemember 58. When the valve 28 is closed by pushing inwardly on handle 66of stem 44 the Wedge members 56, 58 and 60 will all move dovmwardly asshown in FIG- URE 4 until the members 56 and 66 seat on the innersurface of spacer plate 32. Continued movement of valve stem 44 causescenter wedge member 58 to move down wardly with respect to wedge members56 and 60 into the groove 34, thus insuring full seating of the valvestem 44. If the stem 44 breaks or the gate 54 becomes frozen in its seatthe plug 38 can be removed and a tool inserted through opening 36 toforce the gate 54 upwardly.

The outer end of tube 26 has a flange 68 welded thereto for supportinginner member 70 of a packing gland through which passes a non-magneticstainless steel tube 72. Pacfing '74 surrounds the tube 72 and is heldin close engagement therewith by means of an outer packing gland member'76 secured to member 70 by means of capscrews 73. A cooling water inlet86 is secured to the tube 6 adjacent the plate StlR. A magneticdetection head 82 is enclosed in a non-magnetic stainless steel box 84which is secured to the inner end of tube 72. The steel box 84 isgenerally round in cross section, but with its sides cut away to providewater passages 86. The stainless steel parts mentioned above may bereplaced by parts made of other materials which are also non-magnetic,have a high resistivity and can withstand temperatures of approximately1500 F. The detector head 82 consists of an H shaped ferro-magnetic core88 having identical coils 90, 92, 94 and 96 wound on the legs thereofand an excitor coil 98 wound on the cross leg thereof. The coils 90, 92,94 and 96 are connected in electrical series, coils 90 and 94 being inphase with each other and the coils 92 and 96 being in phase with eachother, but out of phase with coils 9i) and 94. Coil 98 is connected to aAC. volt power source L1, L2. The coil 92 is connected by means of lead166 to cathode 102C of thyratron tube 102 through a potentiometer 164.The coil 96 is connected by means of lead 166 to control grid 162G.Capacitor 108 is con nected across the leads 106 and 1196 in parallelwith a rectifier 116, resistor 112 and a milliarneter 114. Potentiometer164 is connected to secondary 116$ of transformer 116, the primary 116Pof which is connected to power source L1, L2. Rectifier 118 is providedin the connection to the secondary 116$. Condenser 129 is connectedacross the leads of secondary 116$. A resistor 122 is pro vided adjacentthe potentiometer 104. The various parts of the thyratron circuit areconventional and are provided for adjustment and sensitivity. A relaycoil 124 is connected to plate 162R The relay coil 124 has a normallyopen contact 124C1 and a normally closed contact 124C1. Relay contact124C1 is connected in series with a red light 126 to power source L1,L2. Relay contact 124C1 is connected in series with a green light 128 topower source L1, L2. A light 130 is connected across relay coil 124 inparallel with a rectifier 132.

The operation of our device is as follows:

With no magnetic material adjacent the detector head 82 the positions ofthe coils 9t 92, 94 and 96 on the H-shaped core 88 is varied until anull point is obtained wherein the output voltage from coils 92 and 96is zero. The coils are firmly fixed on the core in the null position andthe detector head 82 is inserted in the stainless steel container 84which is sealed with a suitable potting compound. The tube 72 With thecontainer 84 mounted thereon is then inserted into the tube 6 with thecoils 90 and 94 preferably being arranged adjacent the strip S as shownin FIGURE 5. It is necessary that one pair of coils 90,

94 or 92, 96 be arranged closer to the strip than the other pair inorder for the apparatus to function. Best sensitivity is obtained whenthe two parallel legs of the core are normal to the strip S. Thedetector may also be located closer to one edge of the strip S than theother edge or it may be centered. The leads L1, L2 and the leads 1% and106 pass through the tube 72 to .the outside thereof with the rest ofthe equipment being supported in any suitable manner in a convenientposition for the operators. As long as the temperature of the strip S isabove the Curie point the bridge circuit will be in balance and thethyratron tube 102 will not conduct, thus contact 12401 will be closedand the light 128 will be on. When the temperature of the strip S isbelow the Curie point the reluctance path through coils 90 and 92becomes less, thus causing an unbalance in the bridge circuit and anoutput signal'is produced, thus causing thyratron tube 182 to conduct.This energizes relay coil 124 and also causes light 130 to light. Thepurpose of the light 1319 is to indicate that the relay 124 isenergized. Energization of relay coil 124 causes contact 1240 to closeand contact 124C1. to open, thus extinguishing light 128 and lightingred light 126. The operator can then slow down the line manually so asto permit the strip to be heated to the annealing temperature. Ifdesired, the signal from the thyratron tube 192 could be used toautomatically control the line speed and thus maintain a correctlyannealed strip.

We have found that the effect on the detector head starts when thetemperature of the strip approaches its Curie point, for example whenthe temperature is 30 below the Curie point.

Other magnetic detectors may be used in place of that shown, but nonehave proved as suitable as the one described above. This detector issensitive, has no moving parts, indicates when the strip approaches theCurie point, is not affected by the usual movement of the strip to andaway from the detector, and has been used as far as eight inches awayfrom the strip.

If it becomes necessary to remove the detector head 82 for repair or forany other purpose the flow of water through inlet 8G is not-interruptedsince otherwise the tube 6 would soon burn out. The container 84 isretracted by means of the tube 72 into tube 26 and the gate 54 is thenclosed, thereby shutting ofi the flow of water to tube 26, but allowingthe water to continue to flow in tube 6. Endplate 70 is then removed,thus allowing detector head 82 to be removed for repair without atanytime interrupting the flow of'cooling water through tube 6. Thereverse procedure is used in replacing the detector head.

While one embodiment of our invention has been shown and described, itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

We claim:

1. Apparatus for determining the magnetic condition of a steel stripbeing continuously heated as it moves longitudinally through a furnacewhich comprises a tube passing through a wall of the furnace into theheating chamber of the furnace adjacent the strip being heated, the axisof said tube being substantially parallel to the path of movement ofsaid strip, a magnetic detector head mounted in said tube in the heatingchamber, a container for said detector head, said tube and containerbeing made of a material which is non-magnetic, has a high resistivityand can withstand temperatures of approximately 1500 F., a gate valveconnected to the end of said tube outside said furnace, a second tubehaving one end connected to said gate valve in axial alignment with saidfirst tube, means closing the second end of said second tube, a thirdtube within said first tube leading from said detector head through saidgate valve, second tube and end closing means to the outside of saidfurnace, and means for circulating coolant through said first tube,whereby the detector head may be removed without interrupting thecirculation of water by moving the detector head to the second tube,then closing the gate valve, and then removing the detector head fromthe second tube.

2. Apparatus for determining the magnetic condition of a steel stripbeing continuously heated as it moves longitudinally through a furnacewhich comprises a tube passing through a wall of the furnace into theheating chamber of'the' furnace adjacent the strip being heated, theaxis of said tube being substantially parallel to the path of movementof said strip, a magnetic detector head mounted in said tube in theheating chamber, a container for said detector head, said tube andcontainer being made of non-magnetic stainless steel, a gate valveconnected to the end of said tube outside said furnace, a second tube.having one end connected to said gate valve in axial alignment with saidfirst tube, a packing gland mounted on the second end of said secondtube and'having an opening therein, a third tube connected to saiddetector head and extending through said opening, said third. tube beingslidably movable in said opening from a position wheresaid detector headis positioned adjacent said strip to a position where said detector headis in said second tube; andmeans for circulating coolant through saidfirst tube.

References Cited in the file of this patent UNITED STATES PATENTS777,750 Sargent Dec. 20, 1904 1,323,824 Brueckner Dec. 2, 1919 1,925,904Mayne Sept. 5, 1933 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patens No: 3,13%;563 April 21', 1964 amp et a1,

rtified that error appears in the above numbered pattion and that thesaid Letters Patentshould read as James B C It is hereby ce entreq'liring oorrec corrected below.

first occurrence read for "124mm Column 2 line 55, 1246 line 56, for"12401" read Signed and sealed this 8th day 0i September 1964,

(SEAL) Atiest:

, ERNEST W. SWIDER EDWARD J BRENNER Anesting Officer Commissioner ofPatents

1. APPARATUS FOR DETERMINING THE MAGNETIC CONDITION OF A STEEL STRIPBEING CONTINUOUSLY HEATED AS IT MOVES LONGITUDINALLY THROUGH A FURNACEWHICH COMPRISES A TUBE PASSING THROUGH A WALL OF THE FURNACE INTO THEHEATING CHAMBER OF THE FURNACE ADJACENT THE STRIP BEING HEATED, THE AXISOF SAID TUBE BEING SUBSTANTIALLY PARALLEL TO THE PATH OF MOVEMENT OFSAID STRIP, A MAGNETIC DETECTOR HEAD MOUNTED IN SAID TUBE IN THE HEATINGCHAMBER, A CONTAINER FOR SAID DETECTOR HEAD, SAID TUBE AND CONTAINERBEING MADE OF A MATERIAL WHICH IS NON-MAGNETIC, HAS A HIGH RESISTIVITYAND CAN WITHSTAND TEMPERATURES OF APPROXIMATELY 1500* F., A GATE VALVECONNECTED TO THE END OF SAID TUBE OUTSIDE SAID FURNACE, A SECOND TUBEHAVING ONE END CONNECTED TO SAID GATE VALVE IN AXIAL ALIGNMENT WITH SAIDFIRST TUBE, MEANS CLOSING THE SECOND END OF SAID SECOND TUBE, A THIRDTUBE WITHIN SAID FIRST TUBE LEADING FROM SAID DETECTOR HEAD THROUGH SAIDGATE VALVE, SECOND TUBE AND END CLOSING MEANS TO THE OUTSIDE OF SAIDFURNACE, AND MEANS FOR CIRCULATING COOLANT THROUGH SAID FIRST TUBE,WHEREBY THE DETECTOR HEAD MAY BE REMOVED WITHOUT INTERRUPTING THECIRCULATION OF WATER BY MOVING THE DETECTOR HEAD TO THE SECOND TUBE,THEN CLOSING THE GATE VALVE, AND THEN REMOVING THE DETECTOR HEAD FROMTHE SECOND TUBE.